1. Field of the Invention
The present invention is directed to a process for depositing thin films in nanometer structures. More specifically, the present invention is directed to a process for depositing thin films in nanometer structures by utilizing supercritical carbon dioxide.
2. Background of the Prior Art
The application of thin films onto surfaces of nanometer structures, such as silicon wafers, microelectrical machines or other semiconductor devices, represents an evolving area of technology. In the past, two methods were primarily utilized to provide this function, chemical vapor deposition and ion sputtering. Both of these methods are highly effective in depositing films on flat surfaces of nanometer structures. However, these methods are not reliable enough when it is desired to provide a thin film coating on the surface of holes, trenches, vias and the like or if the surface to be coated is interrupted by holes, trenches, vias and the like. This is so because the vapor employed in these applications react with the structure to compromise the geometry of the holes, trenches, vias and the like.
The absence of reliability suggests the advisability of a third method of applying a thin film onto surfaces of a nanometer structure characterized by the presence of holes, trenches, vias and the like. This third method, spin coating, involves disposing an aerogel on a surface. The aerogel thereupon solidifies as a thin film. The aerogel is usually dissolved in a solvent and is applied, in spin coating, as a solution. An example of the preparation of an inorganic is illustrated in U.S. Pat. No. 6,140,377. U.S. Pat. No. 6,087,729 exemplifies film forming from inorganic aerogels. Although the problem of changes in nanometer structure geometry resulting from structure reaction with an ionic atmosphere does not arise in spin coating, this method presents its own unique reliability problem when spin coating is utilized in the forming a thin film on a nanometer structure.
This reliability problem resides in the inability to prevent film coating of the sides of the holes, trenches, vias and the like which results in filling the sides of these opening so that the opening is closed. This not only prevents the complete filling of the hole, trench, via and the like but, in addition, prevents the coating of a film on the surface of the base of the hole, trench, via and the like.
The above phenomena is scientifically explained by the relatively high surface tension of the thin film coating. This high surface tension makes it very difficult or even impossible for the film material to penetrate to the bottom of the hole, trench, via or the like. As such, the film material, which cannot penetrate to the bottom of the hole, trench, via or the like, builds up on the top portion of the sides of the hole, trench, via or the like which ultimately results in complete blockage of the opening.
Another problem in the prior art resides in deposition of metals, provide electrical conductivity, in nanometer structures containing trenches, vias and the like. To accomplish this deposition, a metallic seed layer must first be deposited in these holes. Techniques for depositing metallic seed layers, prior to catalyzed electroless deposition of metal, are described in U.S. Pat. Nos. 5,989,787, 6,087,258; and 6,106,722.
The problem associated with filling trenches, vias and the like with a metallic seed layer is identical to the problems associated with filling such holes with an aerogel spin coating. The sidewall deposition of the metallic seed layer often causes the hole to close in on itself prior to the complete filling of the trench, via or the like. The greater the aspect ratio, the more apt it is for this result to occur.
It is therefore apparent that the art is in need of a new process for providing thin films on nanometer structures in those cases where nanometer structures include holes, trenches, vias and the like so that those openings, in the course of coating such structures, do not plug or fill those openings.
A new process has now been developed for depositing thin films on nanometer structures. In this process the thin film is coated onto nanometer structures provided with holes, trenches, vias and the like without the resultant filing of the holes, trenches, vias and the like with the coating material. Instead, this method permits coating of the sides of the hole openings such that the base of the hole is coated without plugging by the coating on the hole""s sides.
Although the invention is not limited to any theory explaining its operation, it is believed that a requirement must be met in order to overcome the difficulties discussed above. That is, a film forming material must be utilized which has a low enough surface tension to permit the fluid to penetrate into very narrow openings. The present invention provides an aerogel composition whose surface tension is low enough to enable the composition to completely coat openings to their bottom without plugging.
In accordance with the present invention a process is provided for deposition of a thin film on a nanometer structure in which a supercritical aerogel material or metallic seed layer, which solidifies into a thin film, is prepared. In this process an aerogel material or a metallic seed layer, which solidifies into a film, is prepared. The aerogel material or metallic seed layer is combined with a supercritical composition to form a supercritical aerogel composition. Thereupon, thermodynamic conditions are adjusted to eliminate supercritical conditions whereupon the supercritical composition is removed and the aerogel material or metallic seed layer solidifies into a solid film.